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Octahedral Bipyridine and Bipyrimidine Dioxomolybdenum( VI ) Complexes: Characterization, Application in Catalytic Epoxidation, and Density Functional Mechanistic Study
Author(s) -
Kühn Fritz E.,
Groarke Michelle,
Bencze Éva,
Herdtweck Eberhardt,
Prazeres Angela,
Santos Ana M.,
Calhorda Maria J.,
Romão Carlos C.,
Gonçalves Isabel S.,
Lopes André D.,
Pillinger Martyn
Publication year - 2002
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20020517)8:10<2370::aid-chem2370>3.0.co;2-a
Subject(s) - chemistry , catalysis , moiety , epoxide , olefin fiber , octahedron , oxygen atom , bipyridine , hydrogen bond , medicinal chemistry , density functional theory , oxygen , alcohol , polymer chemistry , crystallography , stereochemistry , molecule , crystal structure , organic chemistry , computational chemistry
Complexes of the general formula [MoO 2 X 2 L 2 ] (X=Cl, Br, Me; L 2 =bipy, bpym) have been prepared and fully characterized, including X‐ray crystallographic investigations of all six compounds. Additionally, the highly soluble complex [MoO 2 Cl 2 (4,4′‐bis(hexyl)‐2,2′‐bipyridine)] has been synthesized. The reaction of the complexes with tert ‐butyl hydroperoxide (TBHP) is an equilibrium reaction, and leads to Mo V I η 1 ‐alkylperoxo complexes that selectively catalyze the epoxidation of olefins. Neither the Mo−X bonds nor the Mo−N bonds are cleaved during this reaction. These experimental results are supported by theoretical calculations, which show that the attack of TBHP at the Mo center through the X‐O‐N face is energetically favored and the TBHP hydrogen atom is transferred to a terminal oxygen of the Mo=O moiety. After the attack of the olefin on the Mo‐bound peroxo oxygen atom, epoxide and tert ‐butyl alcohol are formed. The latter compound acts as a competitive inhibitor for the TBHP attack, and leads to a significant reduction in the catalytic activity with increasing reaction time.